U.S. patent number 6,118,628 [Application Number 08/594,275] was granted by the patent office on 2000-09-12 for thin film magnetic head with ni-fe alloy thin film.
This patent grant is currently assigned to Hitachi, Ltd.. Invention is credited to Moriaki Fuyama, Takashi Kawabe, Yoshiaki Kita, Kenzo Masuda, Shun-ichi Narumi, Masaaki Sano, Hisashi Takano, Hisano Yamamoto.
United States Patent |
6,118,628 |
Sano , et al. |
September 12, 2000 |
Thin film magnetic head with Ni-Fe alloy thin film
Abstract
A magnetic film having a high saturation magnetic flux density
larger than 1.5 T and a resistivity larger than 40
.mu..OMEGA..cndot.cm is fabricated through an electroplating method
using (40-60)Ni-Fe and by adding Co, Mo, Cr, B, In, Pd or the like
to the (40-60)Ni-Fe. Thereby, it is possible to obtain a recording
head capable of performing sufficient recording in a high frequency
range and to obtain a disk storage system with a high recording
density which has a transfer rate higher than 15 MB/s, a recording
frequency higher than 45 MHz and a rotating speed of a magnetic
disk higher than 4000 rpm.
Inventors: |
Sano; Masaaki (Hitachi,
JP), Kita; Yoshiaki (Hitachinaka, JP),
Narumi; Shun-ichi (Hitachi, JP), Kawabe; Takashi
(Odawara, JP), Fuyama; Moriaki (Hitachi,
JP), Takano; Hisashi (Kodaira, JP),
Yamamoto; Hisano (Hachiouji, JP), Masuda; Kenzo
(Odawara, JP) |
Assignee: |
Hitachi, Ltd. (Tokyo,
JP)
|
Family
ID: |
11922656 |
Appl.
No.: |
08/594,275 |
Filed: |
January 30, 1996 |
Foreign Application Priority Data
|
|
|
|
|
Feb 3, 1995 [JP] |
|
|
7-016666 |
|
Current U.S.
Class: |
360/125.5;
360/125.63; G9B/5.024; G9B/5.08; G9B/5.094; G9B/5.135 |
Current CPC
Class: |
B82Y
10/00 (20130101); B82Y 25/00 (20130101); G11B
5/012 (20130101); H01F 41/26 (20130101); G11B
5/3163 (20130101); G11B 5/3967 (20130101); G11B
5/3109 (20130101); G11B 2005/3996 (20130101) |
Current International
Class: |
G11B
5/012 (20060101); H01F 41/26 (20060101); G11B
5/31 (20060101); H01F 41/14 (20060101); G11B
5/39 (20060101); G11B 005/31 () |
Field of
Search: |
;360/125,126 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Renner; Craig A.
Attorney, Agent or Firm: Antonelli, Terry, Stout &
Kraus, LLP
Claims
What is claimed is:
1. A thin film magnetic head comprising a lower magnetic film, an
upper magnetic film formed on said lower magnetic film, one end of
said upper magnetic film contacting one end of said lower magnetic
film, the other end of said upper magnetic film facing the other
end of said lower magnetic film through a magnetic gap, whereby
said upper magnetic film forms a magnetic circuit including said
magnetic gap together with said lower magnetic film, a conductive
coil having a given number of winding turns passing between both of
said upper and lower magnetic films, wherein at least one of said
upper magnetic film and said lower magnetic film is formed through
a plating method, being made of a Ni-Fe alloy having Ni of 38 to 60
wt % and Fe of 40 to 62 wt % and having a film thickness of 1 to 5
.mu.m, and having sufficient average crystal grain size and a
sufficient magnetic coercive force in a hard axis direction of said
thin film magnetic head for proper operation of said thin film
magnetic head, wherein said average crystal grain size is 100 .ANG.
to smaller than 500 .ANG. and said magnetic coercive force in the
hard axis direction is within a range of 0.5 Oe to lower than 1
Oe.
2. A thin film magnetic head comprising a lower magnetic film, an
upper magnetic film formed on said lower magnetic film, one end of
said upper magnetic film contacting one end of said lower magnetic
film, the other end of said upper magnetic film facing the other
end of said lower magnetic film through a magnetic gap, whereby
said upper magnetic film forms a magnetic circuit including said
magnetic gap together with said lower magnetic film, a conductive
coil having a given number of winding turns passing between both of
said upper and lower magnetic films, wherein at least one of said
upper magnetic film and said lower magnetic film has a sufficient
average crystal grain size, a sufficient resistivity at room
temperature, and a sufficient magnetic coercive force in a hard
axis direction for operation of said thin film magnetic head,
wherein said average crystal grain size is 100 .ANG. to smaller
than 500 .ANG., said resistivity at room temperature is 40 to 60
.mu..OMEGA..cndot.cm, and said magnetic coercive force in the hard
axis direction is within a range of 0.5 Oe to lower than 1 Oe.
3. A thin film magnetic head comprising a lower magnetic core, an
upper magnetic core formed on said lower magnetic core, one end of
said upper magnetic core contacting one end of said lower magnetic
core, the other end of said upper magnetic core facing the other
end of said lover magnetic core through a magnetic gap, whereby
said upper magnetic core forms a magnetic circuit including said
magnetic gap together with said lower magnetic core, a conductive
coil having a given number of winding turns passing between both of
said upper magnetic core and said lower magnetic core, wherein
at least one of said upper magnetic core and said lower magnetic
core is an electroplated thin film made of a Ni-Fe alloy having Ni
of 38 to 60 wt % and Fe of 40 to 62 wt %, and
said at least one of said upper magnetic core and said lower
magnetic core contains a substance composed of at least one of the
group consisting of Co less than 15 wt % Mo less than 3 wt %, Cr
less than 3 wt %. Pd less than 3 wt %, B less than 3 wt % and In
less than 3 wt % in the total weight.
4. A dual element thin film magnetic head for performing writing
and reading of information with individual elements, wherein at
least one of an upper magnetic core and a lower magnetic core of a
writing magnetic core portion of said thin film magnetic head is
made of a metallic magnetic material having a sufficient average
crystal grain size, a sufficient resistivity at room temperature,
and a sufficient magnetic coercive force in a hard axis direction
of said thin film magnetic head for operation of said dual element
thin film magnetic head, wherein said average crystal grain size is
100 .ANG. to smaller than 500 .ANG., said resistivity at room
temperature is 40 to 60 .mu..OMEGA..cndot.cm, and said magnetic
Coercive force in the hard axis direction is within a range of 0.5
Oe to lower than 1 Oe.
5. A dual element thin film magnetic head for performing writing
and reading of information with individual elements with respect to
a magnetic disk wherein at least an upper magnetic core of said
dual element thin film magnetic head for performing recording is
made of a Ni-Fe alloy having Ni of 38 to 60 wt % and Fe of 40 to 62
wt % and having a film thickness of 1 to 5 .mu.m, an average
crystal grain size of 100 .ANG. to smaller than 500 .ANG., a
resistivity at room temperature of 40 to 60 .mu..OMEGA..cndot.cm
and a magnetic coercive force in a hard axis direction within a
range of 0.5 Oe to lower than 1 Oe.
6. A disk storage system comprising a thin film magnetic disk for
recording information, rotating means for rotating said thin film
magnetic disk, a thin film magnetic head for performing writing and
reading of information and being provided on a floating type
slider, transfer means for supporting said floating type slider and
for making access to said thin film magnetic disk, wherein at least
one of an upper magnetic core and a lower magnetic core of a
writing magnetic core portion of said thin film magnetic head is
made of a metallic magnetic material having a sufficient average
crystal grain size, a sufficient resistivity at room temperature
and a sufficient magnetic coercive force in a hard axis direction
for operation of said thin film magnetic head and said disk storage
system, wherein said average crystal grain size is 100 .ANG. to
smaller than 500 .ANG., said resistivity at room temperature is 40
.mu..OMEGA..cndot.cm to 60 .mu..OMEGA..cndot.cm and said magnetic
coercive force in the hard axis direction is within a range of 0.5
Oe to lower than 1 Oe.
7. In a disk storage system comprising a thin film magnetic head,
and a magnetic disk, said thin film magnetic head having a
sufficient average crystal grain size, a sufficient resistivity at
room temperature, and a sufficient magnetic coercive force in a
hard axis direction for operation in the disk storage system, at
least an upper magnetic core of said thin film magnetic head for
performing recording is made of a Ni-Fe alloy, said thin film
magnetic head having a film with a thickness of 1 to 5 .mu.m, said
average crystal grain size is 100 .ANG. to smaller than 500 .ANG.,
said resistivity at room temperature is 40 to 60
.mu..OMEGA..cndot.cm, and said magnetic coercive force in the hard
axis direction is within a range of 0.5 Oe to lower than 1 Oe.
8. In a disk storage system comprising a magnetic disk, and a dual
element thin film magnetic head for performing recording and
reproducing with individual elements, at least an upper magnetic
core of said dual element thin film magnetic head for performing
recording is made of a Ni-Fe alloy having Ni of 38 to 60 wt % and
Fe of 40 to 62 wt % and having a film thickness of 1 to 5 .mu.m, an
average crystal grain size of 100 .ANG. to smaller than 500 .ANG.,
a resistivity at room temperature of 40 to 60 .mu..OMEGA..cndot.cm,
and a magnetic coercive force in the hard axis direction within a
range of 0.5 Oe to lower than 1 Oe.
9. A disk storage system comprising a thin film magnetic disk for
recording information, rotating means for rotating said thin film
magnetic disk, a thin film magnetic head for performing writing and
reading of information and being provided on a floating type
slider, transfer means for supporting said floating type slider and
for making access to said thin film magnetic disk, wherein:
at least one of an upper magnetic core and a lower magnetic core of
said thin film magnetic head is an electroplated thin film made of
a Ni-Fe alloy having Ni of 38 to 60 wt % and Fe of 40 to 62 wt %,
and
said at least one of said upper magnetic core and said lower
magnetic core contains a substance composed of at least one of the
group consisting of Co less than 15 wt %, Mo less than 3 wt %, Cr
less than 3 wt %, Pd less than 3 wt %, B less than 3 wt % and In
less than 3 wt % in the total weight.
10. A disk storage system comprising a thin film magnetic disk for
recording information, rotating means for rotating said thin film
magnetic disk, a dual element thin film magnetic head for
performing writing and reading of information with individual
elements provided on a floating type slider, transfer means for
supporting said floating type slider and for making access to said
thin film magnetic disk, wherein at least one of an upper magnetic
core and a lower magnetic core of a writing magnetic core portion
of said dual element thin film magnetic head is made of a metallic
magnetic material having a sufficient average crystal grain size, a
sufficient resistivity at room temperature, and a sufficient
magnetic coercive force in a hard axis direction for operation of
said dual element thin film magnetic head and said disk storage
system, wherein said average crystal grain size is 100 .ANG. to
smaller than 500 .ANG., and said resistivity at room temperature is
40 .mu..OMEGA..cndot.cm to 60 .mu..OMEGA..cndot.cm.
11. A disk storage system according to claim 10, wherein said at
least one of said upper magnetic core and said lower magnetic core
has said magnetic coercive force in the hard axis direction within
a range of 0.5 Oe to lower than 1 Oe.
12. A disk storage system comprising a thin film magnetic disk for
recording information, rotating means for rotating said thin film
magnetic disk, a thin film magnetic head for performing writing and
reading of information and being provided on a floating type
slider, transfer means for supporting said floating type slider and
for making access to said thin film magnetic disk, wherein said
rotating means provides a sufficient magnetic disk rotation rpm for
operation of the disk storage system, said thin film magnetic head
has a sufficient average crystal grain size, a sufficient
resistivity at room temperature, and a sufficient magnetic coercive
force in a hard axis direction sufficient for operation in the disk
storage system, at least an upper magnetic core of said thin film
magnetic head for performing recording is made of a Ni-Fe alloy
having Ni of 38 to 60 wt % and Fe of 40 to 62 wt % and having a
film thickness of 1 to 5 .mu.m, said average crystal grain size is
100 .ANG. to smaller than 500 .ANG., said resistivity at room
temperature is 40 to 60 .mu..OMEGA..cndot.cm, said magnetic
coercive force in the hard axis direction is 0.5 Oe to lower than 1
Oe.
13. In a disk storage system comprising a thin film magnetic head,
and a magnetic disk, said thin film magnetic head having a
sufficient average crystal grain size, a sufficient resistivity at
room temperature, and a sufficient magnetic coercive force in a
hard axis direction, wherein at least an upper magnetic core of
said thin film magnetic head for performing recording is made of a
Ni-Fe alloy having Ni of 38 to 60 wt % and Fe of 40 to 62 wt % and
having a film thickness of 1 to 5 .mu.m, said average crystal grain
size is 100 .ANG. to smaller than 500 .ANG., and said resistivity
at room temperature is 40 to 60 .mu..OMEGA..cndot.cm.
14. A disk storage system according to claim 13, wherein said
magnetic coercive force in the hard axis direction is within a
range of 0.5 Oe to lower than 1 Oe, a transfer rate of said
magnetic disk and said thin film magnetic head is within a range
larger than 15 mega-bytes per second to 18 mega-bytes per second,
and a magnetic disk diameter of said magnetic disk is within a
range of 1.3 inches to smaller than 3.5 inches, said magnetic disk
being rotated within a range faster than 4000 rpm to 8982 rpm
during recording and reproducing operations, and during recording a
recording frequency being within a range larger than 45 MHz to 80
MHz.
15. A disk storage system according to any one of claims 13, 12 and
14, wherein said upper magnetic core contains a substance composed
of at least one of the group consisting of Co less than 15 S wt %,
Mo less than 3 wt %, Cr less than 3 wt %, Pd less than 3 wt %, B
less than 3 wt % and In less than 3 wt % in the total weight.
Description
BACKGROUND OF THE INVENTION
The present invention relates to a disk storage system, a thin film
magnetic head therefor and a fabrication method thereof.
The present invention relates to a magnetic core for a magnetic
head, and more particularly to a recording head for a dual element
head for a disk system having a high recording density.
In recent years, the recording density of a disk storage system has
become higher and the magnetic coercive force of recording medium
has increased; accordingly, there is a need for a thin film
magnetic head which is capable of sufficiently recording on a
recording medium having a high magnetic coercive force.
In order to realize this, it is necessary to use a material having
a high saturation magnetic flux density (B.sub.S) as a core
material of the magnetic head. In the past, a 80Ni-Fe alloy film of
3 .mu.m thickness has been used for the core material.
However, since the resistivity of the 80Ni-Fe alloy film is as low
as 16 to 20 .mu..OMEGA..cndot.cm, the eddy current loss becomes
large in the high frequency bands. Therefore, the strength of the
recording magnetic field of the magnetic head in a high frequency
band is decreased, and accordingly the recording frequency is
limited to about 30 MHz at maximum.
As an alternative material, Co system amorphous materials and a
Fe-Al-Si sendust alloy thin film are proposed. However, these
materials are not in practical use as yet because the former is
thermally unstable, since the material is amorphous, and the latter
has a disadvantage in the fabrication process as the magnetic core
material for the inductive head, since it requires a high
temperature heat treatment at nearly 500.degree. C.
In recent years, three-element group materials of Co-Ni-Fe have
been proposed (Japanese Patent Application Laid-Open No. Sho
60-82,638, Japanese Patent Application Laid-Open No. Sho 61-76,642,
Japanese Patent Application Laid-Open No. Sho 64-8,605, Japanese
Patent Application Laid-Open No. Hei 2-68,906, Japanese Patent
Application Laid-Open No. Hei 2-290,995).
Although the saturation magnetic flux density (B.sub.S) of these
three-element system materials is as high as 1.5 T, the resistivity
is not large and the crystal grain size is not small in the 80Ni-Fe
alloy; and, in addition to this, there is a disadvantage in the
high frequency characteristic as in the 80Ni-Fe alloy.
On the other hand, the memory capacity of the disk storage system
has been steadily growing year by year, and areal density of a
3.5-inch type disk in production now has been increased up to 350
MB/in.sup.2.
In this case, the data recording frequency is nearly 27 MHz, which
is near the performance limit of a magnetic head using the 80Ni-Fe
alloy film or the Co-Ni-Fe alloy film.
Although there is proposed in Japanese Patent Application Laid-Open
No. 3-68,744 a magnetic film for high frequency use formed by
adding Nb, Ta, Cr, Mo to (40-50) Ni-Fe through a sputtering method,
it is difficult to magnetically form a thick film using a
sputtering method because the material has a large
magnetocrystalline anisotropy.
SUMMARY OF THE INVENTION
One object of the present invention is to provide a disk storage
system, a thin film magnetic head therefor and a fabrication method
thereof wherein
there is provided a disk storage system with a magnetic head for
high density recording in a high frequency band.
Another object of the present invention is to provide a magnetic
head for high density recording in a high frequency band, that is,
a magnetic head which is capable of performing high speed access
and has a high transfer rate.
The present invention has been developed for solving the above
problems, and involves a thin film magnetic head that is mounted on
a disk storage system having a high transfer rate and high
recording density, in which there is a magnetic disk rotated above
4000 rpm when the disk storage system is recording or reproducing,
and in which the recording frequency is not higher than 45 MHz.
It is required that the magnetic core of the write head be made of
a material having a large saturation magnetic flux density
(B.sub.S), a small magnetic coercive force in the hard axis
direction and a large resistivity.
In other words, the range of composition obtainable for a large
resistivity and high saturation magnetic flux density is a range
containing Ni of 38 to 60 wt % for Ni-Fe alloy.
However, when a magnetic film having a thickness of above 2 .mu.m
is usually applied to a thin film magnetic head or the like
fabricated through a sputtering method, the crystal grain size of
the film becomes large, the magnetic coercive force in the hard
axis direction is large and the uniaxial magnetic anisotropy is
hardly induced, since this composition region is in a range where
magnetocrystalline anisotropy is largest.
Therefore, a plating method has been employed in order to suppress
the crystal grain size to a small value, and it has been proposed
to add a third element, such as Co, Mn, Cr, Pd, B, In and the like,
to a base of 38 to 60 wt % Ni-Fe two-element alloy.
The results were found to be a composition range and a fabrication
method of an outstanding thin film having a saturation magnetic
flux density (B.sub.S) larger than 1.5 T, a magnetic coercive force
in the hard axis direction (H.sub.CH) smaller than 1.0 Oe and a
resistivity larger than 40 .mu..OMEGA..cndot.cm, while keeping the
film thickness of 2 to 5 .mu.m which is required for the recording
magnetic field.
By using this material for a thin film magnetic head, it is
possible to provide a high performance disk storage system having
areal density of 500 MB/in.sup.2, a recording frequency of 45 MHz
and a transmission speed of above 15 MB/s.
The present invention is characterized by a disk storage system
comprising a thin film magnetic disk for recording information,
rotating means for the thin film magnetic disk, a thin film
magnetic head for performing writing and reading of information and
provided in a floating type slider, transfer means for supporting
the floating type slider and for making access to the thin film
magnetic disk.
The present invention is characterized by a disk storage system
wherein at least one of an upper magnetic core and a lower magnetic
core the write head is made of a metallic magnetic material having
an average crystal grain size smaller than 500 .ANG., a resistivity
at room temperature larger than 40 .mu..OMEGA..cndot.cm and a
magnetic coercive force in the hard axis direction smaller than 1.0
Oe.
The present invention is characterized by the fact that, in a disk
storage system, at least one of an upper magnetic core and a lower
magnetic core of the writing magnetic core of the write head is an
electroplated thin film made of a Ni-Fe group alloy having Ni of 38
to 60 wt % and Fe of 40 to 62 wt %.
Further, the present invention is characterized by a disk storage
system comprising a magnetic disk having a transfer rate larger
than 15 mega-bytes per second, areal density of recording data
larger than 500 mega-bits per square inch and a diameter smaller
than 3.5 inches.
The present invention is characterized by a disk storage system
wherein the magnetic disk rotates faster than 4000 rpm during
recording and reproducing, the recording frequency is larger than
45 MHz, and at least an upper magnetic core of a thin film magnetic
head for performing the recording is made of a Ni-Fe alloy having
Ni of 38 to 60 wt % and Fe of 40 to 62 wt % and having a film
thickness of 1 to 5 .mu.m, an average crystal grain size smaller
than 500 .ANG., a resistivity of 40 to 60 .mu..OMEGA..cndot.cm and
magnetic coercive force in the hard axis direction smaller than 1.0
Oe, the recording magnetomotive force of the write head being
larger than 0.5 ampere-turns.
The magnetic core in a disk storage system according to the present
invention contains a substance composed of at least one kind of one
of Co less than 15 wt % and Mo, Cr, Pd, B, In less than 3 wt % in
the total weight.
Further, the present invention is characterized by a disk storage
system comprising a thin film magnetic disk for recording
information, rotating means for the thin film magnetic disk, a dual
element head for performing writing and reading of information with
individual elements provided in a floating type slider, and
transfer means for supporting the floating type slider and for
making access to the thin film magnetic disk.
The present invention is characterized by a disk storage system
wherein the magnetic film having the same characteristics and the
same composition as those described above are used for the magnetic
film of the write head.
Furthermore, the present invention is characterized by a disk
storage system comprising a magnetic disk having a transfer rate
larger than 15 mega-bytes per second, areal density of recording
data larger than 500 mega-bits per square inch and a diameter of a
magnetic disk smaller than 3.5 inches.
The present invention is characterized by a disk storage system
wherein the magnetic disk rotates faster than 4000 rpm during
recording and reproducing, the recording frequency being larger
than 45 MHz, a dual element head for performing the recording and
the reproducing with individual elements, the film having the same
characteristics and the same composition as those described above
and being used for at least an upper magnetic core of a write
head.
The present invention is characterized by a thin film magnetic head
comprising a lower magnetic film, an upper magnetic film formed on
the lower magnetic film, one end contacting one end of the lower
magnetic film, the other end facing the other end of the lower
magnetic film through a magnetic gap, whereby the upper magnetic
film forms a magnetic circuit including the magnetic gap together
with the lower magnetic film, and a conductive coil forming a coil
having a given number of winding turns passing between both of the
magnetic films.
The present invention is characterized by a thin film magnetic head
wherein at least one of the upper magnetic film and the lower
magnetic film is formed through a plating method, being made of a
Ni-Fe alloy having Ni of 38 to 60 wt % and Fe of 40 to 62 wt % and
having a film thickness of 1 to 5 .mu.m, an average crystal grain
size smaller than 500 .ANG., and a magnetic coercive force in the
hard axis direction smaller than 1.0 Oe.
The present invention involves a fabrication method of a thin film
magnetic head comprising a lower magnetic film, an upper magnetic
film formed on the lower magnetic film, one end contacting one end
of the lower magnetic film, the other end facing the other end of
the lower magnetic film through a magnetic gap, whereby the upper
magnetic film forms a magnetic circuit including the magnetic gap
together with the lower magnetic film, and a conductive coil
forming a coil having a given number of winding turns passing
between both of the magnetic films.
The present invention involves a fabrication method of a thin film
magnetic head wherein at least one of the lower and the upper
magnetic films is formed by electroplating using a Ni-Fe
electroplating bath containing a metallic ion concentration of
Ni.sup.++ ions of 15 to 20 g/l and Fe.sup.++ ions of 2.0 to 2.7
g/l, the ratio of the Ni.sup.++ ions and the Fe.sup.++ ions
(Ni.sup.++ /Fe.sup.++) being 7 to 8, and containing a stress
release agent and a surface active agent, the pH being 2.5 and
3.5.
Particularly, it is preferable for the thin film magnetic head to
be formed by electroplating though a mask in a magnetic field while
keeping the temperature of the plating bath at 20 to 35.degree. C.
and a current density of 5 to 30 mA/cm.sup.2.
Further, in the present invention, it is preferable that the thin
film magnetic head comprises a magnetic core, the magnetic film
being formed using a plating bath to which is added Co ions of 0.4
to 0.6 g/l and/or Cr, Mo, Pd, In, B less than 0.1 g/l.
Further, it is preferable that the magnetic film of the thin film
magnetic head is formed by electroplating though a mask in a
magnetic field.
In the present invention, writing blur due to the recording
frequency and fluctuation of an over-write value are prevented by
designing the thickness, resistivity and relative permeability of a
magnetic film of a magnetic pole for a write head while taking eddy
current loss into consideration, and at the same time by setting
the data recording frequency to a high value and rotating a
magnetic disk fitted to the above head at a high speed.
(1) It is preferable to provide a means having a transfer rate
higher than 15 mega bytes per second, areal density larger than 500
mega bits per square inch.
(2) It is preferable that when storing of information is performed
using a magnetic disk having a diameter smaller than 3.5 inches,
the magnetic disk is rotated at 4000 rpm during recording and
reproducing, and the recording frequency is set to a value above 45
MHz.
(3) It is preferable to provide a magnetic disk using a metallic
film having a magnetic coercive force larger than 2 kOe.
(4) It is preferable to set the build-up time of the recording
current to a value smaller than 5 nano-seconds (ns).
(5) It is preferable for the coil of an inductive head for
performing recording of information on a magnetic disk to be formed
through a thin film process, for the number of terminals to be
three, and for the inductance between the terminals to be smaller
than 1 micro-henry (.mu.H).
(6) It is preferable for the coil of an inductive head for
performing recording of information on a magnetic disk to be of a
two-layer structure, for the number of winding turns in the first
layer to be equal to that in the second layer, and for the
directions of winding to be opposite to each other.
(7) It is preferable for the coil of an inductive head for
performing recording of information on a magnetic disk to be of a
single-layer structure, and an additional terminal to be connected
to a position (c) corresponding to one-half of the number of
winding turns between the starting point of the coil (a) and the
end point of the coil (b), and for the current flowing between (c)
and (a) and the current flowing between (c) and (b) to be in
opposite phase to each other.
(8) Letting the film thickness of a magnetic film of a core of an
inductive head be d (.mu.m), resistivity be .rho.
(.mu..OMEGA..cndot.cm) and the relative permeability at a low
frequency be .mu., it is preferable to provide a means in which
these parameters satisfy the relation .mu.d.sup.2
/.rho..ltoreq.500.
(9) It is preferable for at least a part of the recording magnetic
pole of a magnetic head used for data recording or data recording
and reproducing to be of a multi-layer structure in which a
magnetic layer and an insulator layer are alternatively laminated,
and for the thickness of the film to be thinner than 2.7 .mu.m.
(10) It is preferable for the Fe-Ni alloy described above to be
used for at least the upper magnetic film of the recording magnetic
films of a magnetic head used for data recording or data recording
and reproducing, and for a Co base amorphous alloy or an Fe base
amorphous alloy to be used for the lower magnetic film.
(11) It is preferable for the material of the recording magnetic
pole contains at least one of Zr, Y, Ti, Hf, Al and Si.
(12) It is preferable for the recording magnetomotive force, that
is, the product of recording current and number of winding turns of
the coil of a magnetic head used for data recording or data
recording and reproducing, to be set to a value larger than 0.5
ampere turns (AT).
(13) It is preferable for the resistivity of at least a part of the
recording magnetic pole of a magnetic head used for data recording
or data recording and reproducing to be larger than 40
.mu..OMEGA..cndot.cm and for the relative permeability to be larger
than 500.
(14) It is preferable for the recording coil of an inductive head
for performing recording of information on a magnetic disk medium
to be of a single-layer structure, for an additional terminal to be
connected to a position (c) corresponding to one-half of the number
of winding turns between the starting point of the coil (a) and the
end point of the coil (b), for the current flowing between (c) and
(a) and the current flowing between (c) and (b) to be in opposite
phase to each other, and for a dual element head using a spin valve
element and a giant magnetoresistive element to be used as the
reproducing head.
In the high frequency band above the recording frequency of 45 MHz,
the head efficiency (efficiency to induce magnetic flux) of the
magnetic head is dominated by the eddy current loss. Although, in
order to decrease the eddy current loss, it is most effective to
decrease the film thickness of the magnetic core, decreasing of the
film thickness causes a recording incapability due to a shortage in
the recording magnetic flux.
In order to sufficiently record on a medium having a high magnetic
coercive force larger than 2000 Oe, particularly above 2300 Oe, the
film thickness is required to be larger than 2 .mu.m and the
saturation magnetic flux density is required to be high. In
general, a multi-layer film may be employed for decreasing the eddy
current loss, but the head process for coping with the high
recording density makes it difficult to obtain a high accuracy in
the dimensions.
Therefore, it is necessary to decrease the eddy current loss by
increasing the resistivity of the magnetic core in order to extend
the frequency characteristic of the permeability (.mu.) of the
magnetic core up to a high frequency.
The Ni-Fe magnetic film (3 .mu.m film thickness) shows a saturation
magnetic flux density (B.sub.S) larger than 1.5 T and a resistivity
(.rho.) of 40 to 50 .mu..OMEGA..cndot.cm when the Ni concentration
is within the range of 38 to 60 wt %. That is, when the Ni
concentration is below 38 wt %, the specific resistivity (.rho.) is
large, but the saturation magnetic flux density (B.sub.S) becomes
lower than 1.5 T.
On the other hand, when the Ni concentration is above 60 wt %, the
saturation magnetic flux density (B.sub.S) also becomes lower than
1.5 T. Especially, it is preferable for the concentration of Ni to
be 40 to 50 wt %.
A plating process is suitable for fabricating a film having such a
composition. That is, since the crystal grain size can be made very
small using an electroplating method, the magnetic coercive force
can be made small and the orientation of the crystal can be
decreased as low as possible even in a case of a composition having
a large magnetocrystalline anisotropy. For example, it is
preferable that the orientation ratio of the crystal is suppressed
below 5.0, that is (1 1 1)/(2 0 0)<5.0.
The composition of a plating bath for fabricating such a film has
Ni and Fe ion concentrations at Ni.sup.++ : 15 to 20 g/l, Fe.sup.++
: 2.0 to 2.7 g/l, and the ion ratio (Ni.sup.++ /Fe.sup.++) at 7 to
8. In this case, the plating current density is 10 to 20
mA/cm.sup.2, the pH is 3.0, and the bath temperature is 30.degree.
C.
On the other hand, in the case of adding at least one of the
elements Co, Mo, Cr, B, In and Pd, it is preferable for the Co to
be less than 15 wt % and for the Mo to be less than 3 wt % in order
to keep the saturation magnetic flux density (B.sub.S) higher than
1.5 T and the resistivity (.rho.) larger than 40
.mu..OMEGA..cndot.cm.
In a case of using Co as a component in the bath, it is preferable
to add up to CoSO.sub.4.6H.sub.2 O of 100 g/l (Co ions of 21 g/l),
and in a case of Mo, Na.sub.2 MoO.sub.4.2H.sub.2 O of 4.8 g/l (Mo
ions of 1.9 g/l). For example, in a case of adding Cr [Cr.sub.2
(SO.sub.4).sub.3.18H.sub.2 O] instead of Mo, the same effect can be
observed In a case of adding B or
In, the resistivity (.rho.) is increased not as much as about
10%.
On the other hand, in the case of adding Co, the saturation
magnetic flux density (B.sub.S) is increased by nearly 10%, though
the resistivity (.rho.) of the film is slightly deceased.
Therefore, it is preferable to use Co together with Mo. Further,
since Co increases the anisotropic magnetic field (H.sub.K), Co is
preferable for stabilizing the magnetic characteristic.
When Co is added in an amount more than 15 wt %, the saturation
magnetic flux density (B.sub.S) of the film is increased, but the
resistivity (.rho.) of the film is deceased too much. Therefore,
the resistivity (.rho.) of the film cannot be increased up to a
desired value unless a large amount of Mo, Cr are added.
This is not preferable because the magnetic coercive force of the
film becomes large. In order to increase the resistivity (.rho.)
without increasing the magnetic coercive force of the film, the
amount of Mo, Cr to be added should be limited to 3 wt % or
less.
In the case of adding B, In, Pd or the like, the amount added
should be limited as indicated above. In these cases, the plating
condition may be the same as in the case of a Ni-Fe magnetic film,
as described above.
Assuming that the high frequency loss (tan .delta.) of the magnetic
film is attributed only to the eddy current loss, the high
frequency loss can be expressed by the following equation.
where .mu.' and .mu." are a real part and an imaginary part of the
complex magnetic permeability. C is a constant determined by the
shape of the film, and .mu..sub.0 is the permeability of a
vacuum.
From the above equation (1), when the relative permeability .mu.
inherent in the magnetic film, the film thickness d, and the
resistivity .rho. are given, the eddy current loss tan .delta.
corresponding to the frequency f can be obtained. Since the change
of the head efficiency (efficiency to induce magnetic flux)
corresponding to the frequency is proportional to the change in the
real part of the complex permeability, the frequency dependence of
the head efficiency can be obtained by calculating .delta. from
Equation (1) and taking the cosine component.
That is, the head efficiency .eta. for each frequency can be
expressed by the following equation.
From Equation (2), by specifying the value .mu.d.sup.2 /.rho. which
can be obtained from the relative permeability .mu. inherent in the
magnetic film, the film thickness d and resistivity .rho., the head
efficiency .eta. for an arbitrary frequency f can be
extrapolated.
By combining the above head and a magnetic disk using a metallic
magnetic film having a magnetic coercive force larger than 2 kOe,
which exhibits a small write blurring during high frequency
recording and a small fluctuation of overwriting, it is possible to
obtain a high performance disk storage system having areal density
larger than 500 MB/in.sup.2, a recording frequency higher than 45
MHz and a transfer rate higher than 15 MB/s.
In a case of using a fast and wide SCSI (Small Computer System
Interface) having a data bus of two-byte width as an I/O interface,
from the relationship between the price of an input/output device
and a transfer rate per one magnetic disk device composing the
input/output device, it is possible to transmit data up to 20 MB/s
at a maximum when the fast and wide SCSI having a data bus of
two-byte width as an I/O interface is used.
In this case, when the transfer rate per one magnetic disk device
is above 15 MB/s, it can be understood that the price of the
input/output device can be decreased.
Further, when the capacity per one magnetic disk device is 550 MB,
it is possible to employ an OS (Operation Software) such as
Windows, Workplace and the like. In order to realize this capacity
with one magnetic disk of 3.5 inch type, areal density capable of
recording the data is required to be 500 MB/in.sup.2.
According to the present invention, a recording head, which is
capable of performing sufficient recording to a medium having a
high magnetic coercive force and at a high frequency range, is
fabricated by a specified composition and through a low cost
electroplating method.
Thereby, it is possible to obtain a disk storage system with a high
recording density capable of a high data transfer rate, decreasing
access time and increasing memory capacity by keeping a transfer
rate higher than 15 MB/s, a recording frequency higher than 45 MHz,
and the rotating speed of the magnetic disk higher than 4000
rpm.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is a perspective view showing a disk storage system;
FIG. 2 is cross-sectional view showing a disk storage system;
FIG. 3 is a front view showing a portion of the disk storage
system;
FIG. 4 is a top plan view showing a portion of the disk storage
system;
FIG. 5 is a side view of a magnetic head and a supporting
device;
FIG. 6 is a top view of a magnetic head and a supporting
device;
FIG. 7 is a perspective view showing a slider having a thin film
magnetic head;
FIG. 8 is a perspective view showing a dual element head;
FIG. 9 is a graph showing the relationship between frequency and
overwrite;
FIG. 10 is a graph showing the relationship between crystal grain
size and magnetic coercive force in the hard axis direction;
FIG. 11 is a cross-sectional view showing an inductive head;
FIG. 12 is a plan view showing an inductive head;
FIG. 13 is a plan view showing the construction of a film of a
magnetoresistive head;
FIG. 14 is a perspective view showing the construction of a film of
a magnetoresistive head;
FIG. 15 is a perspective view showing the construction of a film of
a magnetoresistive head;
FIG. 16A is a graph showing the relationships between content of Ni
or (Ni/Fe) ratio and B.sub.S ;
FIG. 16B is a graph showing the relationships between content of Ni
or (Ni/Fe) ratio and .rho.;
FIG. 16C is a graph showing the relationships between content of Ni
or (Ni/Fe) ratio and H.sub.CH ;
FIG. 17A is a graph showing the relationship between content of Mo
and B.sub.S ;
FIG. 17B is a graph showing the relationship between content of Mo
and .rho.;
FIG. 17C is a graph showing the relationship between content of Mo
and H.sub.CH ;
FIG. 18A is a graph showing the relationship between content of Mo
and B.sub.S ;
FIG. 18B is a graph showing the relationship between content of Mo
and .rho.;
FIG. 18C is a graph showing the relationship between content of Mo
and H.sub.CH ;
FIG. 19 is a graph showing the relationship between frequency and
(.mu.f/.mu..sub.1 MHz);
FIG. 20 is a plan view showing a thin film magnetic head;
FIG. 21 is a cross-sectional view showing a thin film magnetic
head;
FIG. 22 is a perspective view showing a dual element head; and
FIG. 23 is a plan view showing an inductive head.
DESCRIPTION OF THE INVENTION
Hereinafter, various embodiments of a disk storage system, a thin
film magnetic head therefor and a fabrication method thereof
according to the present invention will explained with reference to
the drawings.
FIG. 1 and FIG. 2 are a perspective view and a plan view showing an
embodiment of a disk storage system in accordance with the present
invention. The disk storage system is composed of a magnetic disk 1
for recording information, a DC motor (not shown in the figures)
operating as a means to rotate the magnetic disk, a magnetic head 2
for writing and reading information, a positioning device operating
to support the magnetic head 2 and to change the position of the
magnetic head 2 with respect to the magnetic disk 1, which
positioning device is composed of an actuator 4, a voice coil motor
5 and an air filter 6 for keeping the inside of the system
clean.
The actuator 4 is composed of a carriage 7, a rail 8, and a bearing
9. The voice coil motor 5 is composed of a voice coil 10 and a
magnet 11. These figures show an example wherein eight magnet disks
are attached to a single rotating shaft to make the memory capacity
large.
FIG. 3 is a front view of a disk storage system in accordance with
the present invention, and FIG. 4 is a plan view of the disk
storage system. In the figures, the reference character 1 denotes a
magnetic disk, the reference character 2 denotes a magnetic head,
the reference character 3 denotes a gimbal system supporting
device, and the reference character 4 denotes a positioning device
(actuator).
The magnetic disk 1 is rotated in the direction of the arrow a by a
rotating driving mechanism. The magnetic head 2 is supported by the
supporting device 3 and is moved in the direction of the arrow
b.sub.1 or b.sub.2 on the rotating diameter O.sub.1 so as to be
positioned, and thereby magnetic recording or reproducing is
performed using a proper one of the cylinders T.sub.1 to
T.sub.n.
The magnetic disk 1 is a medium having a surface roughness
R.sub.MAX less than 100 .ANG., preferably a medium having a better
surface condition of surface roughness less than 50 .ANG..
The magnetic disk 1 is made by forming a magnetic recording film on
the surface of a rigid substrate through a vacuum film forming
method. The magnetic recording film is formed as a magnetic thin
film made of .gamma.-Fe.sub.2 O.sub.3 or Co-Ni, Co-Cr or the
like.
Since the film thickness of the magnetic recording film formed
through the vacuum film forming method is thinner than 0.5 .mu.m,
the surface characteristic of the rigid substrate directly reflects
on the surface characteristic of the recording film.
Therefore, a rigid substrate having a surface roughness R.sub.MAX
which is less than 100 .ANG. is used. A rigid substrate having a
major component of glass, chemically reinforced soda-alumina
silicate glass or ceramic is suitable for such a rigid
substrate.
The magnetic recording film may be formed of a magnetic iron oxide,
such as .gamma.-Fe.sub.2 O.sub.3 or the like, or a magnetic
nitride. In a case where the magnetic film is a metal or an alloy,
it is preferable for an oxide film or a nitride film to be provided
on the surface or an oxide covering film to be formed on the
surface. It is also preferable to use a carbon protecting film.
By doing so, the durability of the magnetic recording film is
improved and accordingly the magnetic disk 1 is protected from
damage, which may be caused in a case where recording or
reproducing is performed under a very low floating condition or at
a contact-start-stop condition.
The oxide film or the nitride film may be formed through reactive
sputtering, reactive vapor depositing or the like. The oxide
coating film may be formed by intentionally oxidizing the surface
of a magnetic recording film made of a metal or an alloy containing
at least one kind of iron, cobalt and nickel, such as Co-Ni or
Co-Cr, through reactive plasma treatment or the like.
The magnetic disk 1 may be either of perpendicular recording type,
where the recording residual magnetization in the magnetic
recording film has a component in the perpendicular direction with
respect to the film surface as a major component, or of the
longitudinal recording type, where the recording residual
magnetization has a longitudinal component as a major
component.
It is also possible to apply a lubricant on the surface of the
magnetic recording film though this is omitted in the figure.
FIG. 5 and FIG. 6 are views showing the assembled construction of
the magnetic head 2 and the gimbal system supporting device 3.
The magnetic head 2 has reading and writing elements 22 in the side
of an air flow-out end of a slider 25 of a ceramic structure body
and is supported by the supporting device 3 driven by a positioning
device 4 so as to be allowed a pitching motion and rolling motion
by adding a load on the surface 24 opposite to a floating surface
23. The reading and writing element 42 is a thin film element
formed through the same process as that of IC fabricating
technology.
The supporting device 3 is constructed by attaching and fixing one
end of a supporting body 37, formed of an elastic metallic thin
film, to a rigid arm part 51 attached to the positioning device 4
using jointing members 11, 12, and by attaching a flexible body 36,
formed of a similar metallic thin film, to a free end on the other
end in the lateral direction of the supporting body 37, and by
attaching the magnetic head 2 on the underside surface of the
flexible body 36 (refer to FIG. 3 and FIG. 4.
The portion of the supporting body 37 attached to the rigid arm
part 51 has an elastic spring part 41, and a rigid beam part 42 is
connected to the elastic spring part 41. The rigid beam part 42 has
flanges 42a, 42b formed by bending up both sides.
The flexible body 36 comprises two outer flexible frame parts 31,
32 extending nearly in parallel to the axial line in the lateral
direction of the supporting body 36, and a side frame 33 joining
the outer flexible frame parts 31, 32 in the end opposite the
supporting body.
The flexible body 36 comprises further a middle tongue-shaped part
34 having one end forming a free end extending from near the middle
portion of the side frame 33 along and nearly in parallel to the
side flexible frame, and the one end at the opposite side to the
side frame 33 is attached to the vicinity of the free end of the
supporting body 37 by welding or the like.
On the upper surface of the middle tongue-shaped part 34 of the
flexible body 36, a projection 35 for load, for a example, a
semi-spherical projection is provided, and a load is transmitted
from the free end of the supporting body 37 to the middle
tongue-shaped part 34. The surface 24 of the magnetic head 2 is
fixed to the under surface of the middle tongue-shaped part 34 by
an adhesive.
In this embodiment, a magnetic disk 1 having a surface roughness
R.sub.MAX is used and the floating amount g at the starting of
floating the magnetic head 2 is set within the range of 0.01 .mu.m
to 0.04 .mu.m.
The floating amount g of the innermost cylinder T.sub.n among the
reading and writing cylinders T.sub.1 to T.sub.n provided in the
magnetic disks 1 is set between the floating amount g at the
starting of floating of 0.01 .mu.m to 0.04 .mu.m and a value
several times that of the floating amount.
The shape of the slider 21 constructing the magnetic head 2, the
load applied from the supporting device 3 to the magnetic head 2,
the rotating speed of the magnetic disk 1 and so on are set so as
to obtain the floating amount as described above.
FIG. 7 is a perspective view showing a negative pressure slider.
The load slider 70 comprises an air intake surface 71 and a
negative pressure generating surface 73 surrounded by two positive
pressure generating surfaces 72, 72 for generating a floating
force, and a groove 74 having a step larger than the negative
pressure generating surface 73 in the boundary between the air
intake surface 71, the two positive pressure generating surfaces
72, 72 and the negative pressure generating surface 73.
On an air outlet end 75, the negative pressure slider 70 also has
thin film magnetic head elements 76 for recording and reproducing
information on and from a magnetic disk 1.
During floating of the negative pressure slider 70, the air
introduced through the air intake surface 71 is expanded at the
negative pressure generating surface 73. At that time, since an air
flow flowing toward the groove 74 is also generated, there exists
inside the groove 74 an air flow
flowing from the air intake surface 71 toward the air outlet end
75.
Therefore, dust floating in the air is forced to flow by the air
flow inside the groove 74 and is exhausted from the air outlet end
78 to the outside of the negative pressure slider 70 even if the
dust floating in the air enters through the air intake surface 71
during floating of the negative pressure slider 70.
Further, since there is an air flow, stagnation inside the groove
74 during floating of the negative pressure slider 70 is avoided,
and dust is not accumulated inside the groove 74.
FIG. 8 is a conceptual view of a dual element head forming a
recording head. The dual element head comprises an inductive head
and a reproducing head, and a shield part is provided for
preventing disturbance in the reproducing head due to leakage
magnetic flux.
Although mounting of the recording head for a perpendicular
magnetic recording is shown in this embodiment, the
magnetoresistive element according to the present invention may be
used for a perpendicular recording by combining it with a head for
vertical magnetic recording.
The head is formed with a reproducing head composed of a lower
shield film 82 on a substrate 80, a magnetoresistive film 86, an
electrode 85 and an upper shield film 81, and a recording head
composed of a lower magnetic film 84, a coil 87 and an upper
magnetic film 83.
By using this head, signals are written on the recording medium and
signals are read out from the recording medium. The magnetic gap
between the sensing part of the reproducing head and the recording
head can be positioned at the same track at the same time by
forming it at an overlapping position on the same slider, as
described above. This head is formed in a slider and mounted on a
disk storage system.
In this embodiment, the upper and the lower magnetic films of the
inductive head are formed through the following fabrication
method.
There is fabricated an inductive head having upper and lower
magnetic cores which are electroplated in a plating bath containing
Ni.sup.++ of 16.7 g/l, Fe.sup.++ of 2.4 g/l, and a common
stress-release agent and a surface active agent under a condition
of pH of a 3.0 and a plating current density of 15 mA. The track
width is 4.0 .mu.m, and the gap length is 0.4 .mu.m.
The composition of this magnetic film is 42.4 Ni-Fe (wt %), and as
to the magnetic characteristics, the saturation magnetic flux
density (B.sub.S) is 1.64 T, the magnetic coercive force in the
hard axis direction (H.sub.CH) is 0.5 Oe, the and resistivity
(.rho.) is 48.1 .mu..OMEGA..cndot.cm.
The inductive head comprises an upper magnetic core 83, a lower
magnetic core 84 which also serves as an upper shield film, a coil
87, a magnetoresistive element 86, an electrode 85 for conducting a
sense current to the magnetoresistive element, a lower shield film
82 and a slider 80.
FIG. 9 shows the evaluated result of the performance (over-write
characteristic) of the recording head according to the present
invention having such a construction. An outstanding recording
characteristic of nearly -50 dB in a high frequency range above 40
MHz has been obtained.
FIG. 10 shows the relationship between the magnetic coercive force
in the hard axis direction and the average crystal grain size of
magnetic films obtained through the plating method and the
sputtering method in this embodiment. It can be understood that
when the average crystal grain size is smaller than 500 .ANG., low
magnetic coercive force lower than 1.0 Oe can be obtained.
Further, for the lower magnetic film, a Ni-Fe alloy thin film
composed of Ni 70 to 80 wt % and Fe comprising the remainder, may
be formed through electroplating, in the same way as described
above, or the alloy film may be also formed through a sputtering
method.
FIG. 11 is a cross-sectional view and FIG. 12 is a plan view
showing an inductive head according to the present invention. The
thin film head comprises an upper shield film 81, a lower magnetic
film 83 attached onto the upper shield film and an upper magnetic
film 84 which are made of the aforementioned magnetic film.
FIG. 11 is a cross-sectional view taken on the plane of the line
A--A of FIG. 12. A non-magnetic insulator body 89 is disposed
between layers 83, 84. A part of an insulator body determines a
magnetic gap 88, and this interacts in a conversion relationship
with, for example, a magnetic medium placed in an air-bearing
relation, as in the prior art.
The supporting body 80 serves as a slider having an air-bearing
surface (ABS), and this accesses and is in a floating relation with
respect to a rotating disk during disk file operation.
The thin film magnetic head has a back gap 90 formed by an upper
magnetic film 83, a lower magnetic film 84. The back gap 90 is
separated from the magnetic gap by a coil 87 interposed
between.
The continuing coil 87 forms a layer on the lower magnetic film 84,
for example, through plating to electromagnetically couple with the
lower magnetic film. The coil 87 has an electric contact point 91
in the center of coil which is buried with insulator body 89, and
also has a large area serving as an electric contact point 92 in
the outer end terminal point of the coil. The contact points are
connected to external lead wires and a reading and writing signal
processing head circuit (not shown).
In accordance with the present invention, the coil 87 formed in a
single layer has a slightly deformed elliptical shape, and the
portion having a small cross-sectional area is placed in the
nearest position to the magnetic gap and the cross-sectional area
gradually increases as the distance from the magnetic gap
increases.
The back gap 90 is positioned relatively near the ABS of the
magnetic gap. However, there exists relatively densely many
windings of the elliptical coil between the back gap 90 and the
magnetic gap 88, and the width or the cross-sectional diameter of
the coil is small in this region. The large cross-sectional
diameter in the farthest region from the magnetic gap decreases the
electrical resistance.
The elliptical coil does not have any angle or sharp corner or
edge, and therefore resistance to current is small. Further, the
total length of the conductor of the elliptical coil is short
compared with a rectangular or a circular (ring-shaped) coil.
Due to these advantages, the total resistance of the coil is
relatively small, and consequently heat generation is small and
heat is properly radiated. Since heat generation is substantially
decreased, collapse, extension and expansion of the thin film are
prevented and the cause of ball-tip projection is eliminated.
The shape of the elliptical coil, the width of which uniformly
changes, can be formed through a conventional economical
technology, such as a sputtering or vapor deposition method.
In a coil having a different shape, particularly a shape having
corners, plating deposition is apt to become non-uniform in width.
A coil having removed corners or sharp edge portions is subjected
to a small mechanical stress.
In accordance with this embodiment, a nearly elliptical coil having
multiple winding turns is formed between the magnetic cores, the
cross-sectional diameter of the coil gradually expands from the
magnetic gap toward the back gap, the signal output power is
increased and the heat generation is decreased.
FIG. 13 is a conceptual view showing the construction on the
surface of a substrate of a magneto-resistance effect element in
accordance with the present invention, when formed on the bottom
portion of the above mentioned inductive head.
The magnetoresistive film 110 is formed along a surface 163 opposed
to a recording medium in a long rectangular shape having a length
143 of the element on a substrate 150. This definition of the shape
has an effect to provide a proper shape magnetic anisotropy in the
perpendicular direction with respect to a direction 180 in which
the magnetic field to be detected by the magnetoresistive film 110
is applied.
A current is conducted in the magnetoresistive film 110 from
electrodes 140 electrically contacting the film, and an output is
obtained from the resistance change of the film caused by the
magnetic field applied to the magnetic field detecting portion
having a width 141 in the direction parallel to and the width 142
in the direction perpendicular to the surface of the recording
medium 191.
Although in this conceptual view the end portions of the
magnetoresistive element are exposed to the opposite surface of the
recording medium, the mechanical durability of the element can be
increased by arranging a yoke-shaped soft magnetic body on the
opposite surface to guide the magnetic field from a recording
medium and by magnetically coupling to a magnetoresistive element
arranged inside.
Especially, the resistance of the magnetic circuit is reduced and
the sensitivity can be improved by decreasing the MR height of the
element.
The magnetoresistive element according to the present invention has
a construction, for example, as shown in FIG. 14. The
magnetoresistive element is formed by laminating on a substrate 150
a magnetoresistive film 110, that is, a film consisting of a bias
film 132, a magnetic film 111, a non-magnetic conductive film 120,
a magnetic film 112, a non-magnetic conductive film layer 120, and
a magnetic film layer 111, with a bias film 131, and further
disposing an electrode 140 on the laminated layer by electrical
joining.
In the construction of the element shown in FIG. 12, an electrode
140 is placed under a bias film 131. This is an example of an
effective construction in a case where an insulator film, such as
nickel oxide film, is used for the upper bias film.
Another construction of the electrode may be formed in such a
manner, for example, that a bias film is partially formed and then
an electrode is formed over the bias film. There are still other
methods where a conductive bias film, for example, a Fe-Mn film, a
Co-Pt film or the like, is formed and then an electrode is formed
directly on the conductive bias film.
The present element is constructed by alternatively laminating a
magnetic film applied with a strong anisotropy by a bias film, a
magnetic film applied with a weaker anisotropy than the above
anisotropy by uniaxial magnetic anisotropy, a shape magnetic
anisotropy or a soft film bias through a non-magnetic conductive
film so as to conduct current to each other but not cause magnetic
coupling between them. Especially, the direction of application of
the anisotropy will be described below.
FIG. 15 is a conceptual view showing an example of anisotropy
control in a magnetoresistive element in accordance with the
present invention, and is a perspective view of a part of the
element shown by A-A' in FIG. 14.
The bias films 131 and 132 apply anisotropy by switched connection
in the directions indicated by the arrows 171 and 172 in the
figure. The arrow 160 in the figure indicates the direction of the
magnetic field to be detected, and the arrow 161 indicates the
direction of unidirectional magnetic anisotropy induced in the
magnetic film 111.
The easy magnetizing of the magnetic film 112 sandwiched by the
non-magnetic conductive films 120 is in the direction indicated by
the arrow 162 in the figure by induction of uniaxial magnetic
anisotropy. This can be attained by applying a magnetic field in a
proper direction during the growing of the magnetic film.
The embodiment shown by the figure is an example in which the
application of the anisotropy is attained by the bias film and the
inductive magnetic anisotropy. As a result, the arrows 161 and 162
intersect at a right angle with each other on the surface of the
film.
By setting the anisotropy of the magnetic film 111 to be larger and
anisotropy of the magnetic film 112 to be smaller than the
magnitude of the magnetic field to be detected, the magnetization
of the magnetic film 111 can be fixed to a nearly constant value
and only the magnetization of the magnetic film 111 can largely
react to an external magnetic field.
Further, the magnetization of the magnetic film 111 is in a state
of easy axis excitation with respect to the magnetic field to be
detected where the directions of the magnetization and the external
magnetic field are parallel to each other due to anisotropy
161.
On the other hand, the magnetization of the magnetic film 112 is in
a state of hard axis excitation where the directions of the
magnetization and the external magnetic field are perpendicular to
each other. With this effect, the response described above becomes
even more outstanding.
In addition to this, the element becomes capable of operating at a
high frequency since a state is reached where the element is driven
by an external magnetic field in the hard axis excitation direction
due to rotation of the magnetization of the magnetic film 112 with
respect to the direction of the arrow 162 as an origin, and
accordingly the noise accompanied by excitation of movement of the
magnetic domain wall is prevented.
There is another embodiment of a magnetoresistive element in which
the application of anisotropy is performed by two different kinds
of bias films, that is, an anti-ferromagnetic film and a
hard-magnetic film.
The magnetoresistive element is formed by laminating on a substrate
150 an anti-ferromagnetic film 132, a magnetic film 111, a
non-magnetic film 120, a magnetic film 112 and a hard-magnetic film
133, and then by connecting an electrode on the laminated film.
Both of the anti-ferromagnetic film 132 and the hard-magnetic film
133 are respectively fixed to two of the magnetic films 111, 112
separated by the non-magnetic film.
The directions of magnetization of the magnetic films 111 and 112
are induced in the directions indicated by the arrows 161 and 162
respectively by performing thermal treatment under a magnetic field
or magnetizing treatment in the directions 172 and 173, a parallel
direction and a perpendicular direction to the direction 160 of the
magnetic field to be detected.
The anti-ferromagnetic film is formed of, for example, a nickel
oxide, and the hard-magnetic film is formed of a cobalt-platinum
alloy. The same effect may be obtained when the positions of the
hard-magnetic film and the anti-ferromagnetic film are reversed, or
the directions of induced magnetization are reversed.
The films composing the magnetoresistive element according to the
present embodiment are fabricated using a high frequency magnetron
sputtering apparatus in a manner indicated as follows.
Magnetoresistive elements have been fabricated by successively
laminating the following materials on a ceramic substrate and a Si
single crystal substrate of 1 mm thickness and 3 inches diameter in
an argon atmosphere of 3 mill-Torrs. As a sputtering target,
targets of nickel oxide, cobalt, a nickel-20 at % iron alloy and
copper are used.
The addition of cobalt to nickel-20 at % iron is preformed by
placing a cobalt chip on a nickel-20 at % iron target. The addition
of nickel and iron to cobalt is performed by placing nickel and
iron chips on a cobalt target.
The laminated film is formed by applying high frequency electric
power to each cathode while placing each of the targets so as to
generate a plasma inside the system and then by opening and closing
a shutter provided for each of the cathodes one by one to form each
of the films successively.
During the forming of the films, a magnetic field of approximately
50 Oe is applied in parallel to the substrate using two pairs of
magnets crossing at right angle to each other on the surface of the
substrate to form an uniaxial magnetic anisotropy in the film and
to induce the direction of the switched connection bias of a nickel
oxide film to each direction.
The induction of anisotropy is performed by applying a magnetic
field in the direction to be induced during the forming of each
magnetic film using two pairs of magnets provided near a substrate.
Otherwise, the anti-ferromagnetic bias is induced in the direction
of a magnetic field by performing heat treatment under a magnetic
field at a temperature near the Neel temperature of the
anti-ferromagnetic film after forming the multi-layer film.
An evaluation of performance of the magnetoresistive element is
conducted by patterning the film in a rectangular shape and forming
electrodes. At this time, the patterning and electrode forming are
performed so that the
direction of the uniaxial magnetic anisotropy of the magnetic film
becomes parallel to the direction of the current in the
element.
The measurement is performed by conducting a constant current
between the electrode terminals, applying a magnetic field in the
surface of the element in the direction perpendicular to the
direction of current flow, measuring the electrical resistance of
the element using the voltage between the electrode terminals, and
detecting the measured results as the magnetoresistance ratio.
In Table 1, the characteristic of the element is expressed by the
magnetoresistance ratio and the saturation magnetic field. The
reproducing output of the element corresponds to the largeness of
the magnitude of the magnetoresistance ratio and the sensitivity
corresponds to the smallness of the magnitude of the saturation
magnetic field.
It is clear from the result of Table 1 that the magnetoresistive
elements No. 1 to No. 5 have a magnetoresistance ratio larger than
4% and a better magnetic characteristic, and are outstanding
particularly in the resistance changing rate compared to No. 6 and
No. 7.
Among them, the specimen No. 1, No. 2 and No. 4 show an excellent
magnetic field sensitivity of about 10 Oe saturation magnetic field
and a high output of 6 to 7% magnetoresistance ratio.
TABLE 1 ______________________________________ Spe.
Composition/Thickness of film (.ANG.) MS H.sub.S
______________________________________ No. 1
NiO/FiFe/Cu/NiFe/Cu/NiFe/NiO 6.5 12 300/ 60 /21/ 40 /21/ 60 /300 2
NiO/Co/Cu/NiFe/Cu/Co/NiO 7.2 13 300/50/21/ 40 /21/50/300 3
NiO/NiFe/Cu/NiFe/Cu/NiFe/Cu/NiFe/NiO 5.5 11 300/ 60 /21/ 40 /21/ 40
/21/ 60 /300 4 NiO/Co/Cu/Co/NiFe/CO/Cu/Co/NiO 7.5 16 300/60/21/15/
40 /15/21/60/300 5 NiO/NiFe/Cu/NiFe 4.5 15 300/ 60 /21/ 40 6
NiFe/Cu/NiFe/NiO 3.0 14 60 /21/ 40 /300 7 NiFe/Cu/NiFe/NiO 3.9 10
60 /21/ 40 /150 ______________________________________ Note Spe.:
specimen Mr: magnetoresistance ratio (%) H.sub.S : saturation
magnetic field (Oe)
In the disk storage system of the present embodiment, the region
sandwiched by a pair of electrodes 85, which region represents the
reproducing track width, is set to 2 .mu.m. During recording, a
current of 15 mA.sub.op is conducted to the coil 87 having 20
winding turns to record any information on a medium.
On the other hand, during reproducing, a direct current of 8 mA is
conducted to the lead wire to detect leakage magnetic field from
the medium.
A disk storage system is constructed by combining this magnetic
head with a 3.5 inch magnetic disk having a CoCrTa (adding amount
of Cr is 16 at %) recording film with a magnetic coercive force in
the recording bit direction of 2100 Oe and a magnetic coercive
force orientation ratio of 1.2.
The production Br.cndot..delta. of the residual magnetic flux
density and the film thickness of the magnetic disk recording film
used is 100 Gauss.cndot..mu.m. The specification of the magnetic
memory apparatus constructed in accordance with this embodiment is
shown in Table 2.
TABLE 2 ______________________________________ Specification if a
3.5 inch Type Apparatus using a Dual Element Head
______________________________________ Memory Capacity 5.5 GB
Number of Disks 4 Number of Data Surfaces 8 Number of Heads 8
Number of Tracks/Disk Surface 7378 Maximum Linear Recording Density
170 kBPI Track Density 8.3 kTPI Rotating Speed 4491 RPM Recording
Frequency 86.0 MHz Transfer Rate (to/from Media) 18 MB/sec
______________________________________
FIGS. 16A, 16B and 16C are graphs showing the relationships between
a component of magnetic film, magnetic characteristics and
resistivity (.rho.) when metallic ion concentrations, that is,
amounts of Ni.sup.++ and Fe.sup.++, in a plating bath are
varied.
Ni.sup.++ is added using NiCl.sub.2.6H.sub.2 O, Fe.sup.++ is added
using FeSO.sub.4.7H.sub.2 O, and a common stress release agent and
a surface active agent are added. Plating is performed under a
condition of pH of 3.0 and plating current density of 15
mA/cm.sup.2. The film thickness is 3.0 .mu.m.
It can be understood that when the content of Ni in the film is
within the range of 38 to 60 wt %, the saturation magnetic flux
density (B.sub.S) is larger than 1.5 T and the resistivity (.rho.)
is larger than 40 .mu..OMEGA..cndot.cm, that is, the film has
outstanding characteristics in that the saturation magnetic flux
density (B.sub.S) is 1.5 times as large and the resistivity (.rho.)
is twice as large as those of the well known 80Ni-Fe permalloy
film.
Further, the magnetic coercive force in the hard axis direction
(H.sub.CH) is smaller than 1 Oe, similar to 80Ni-Fe permalloy. The
varying trends of saturation magnetic flux density (B.sub.S) and
resistivity (.rho.) are nearly the same as those of the bulk
material, but the decreasing rates as the Ni content increases are
smaller than those of the bulk material. The reason is that the
film has a very small crystal grain size of 40 to 80 .ANG. compared
with that of the bulk material.
Such characteristics are not largely varied when the pH is varied
within the range of 2.5 to 3.5, and the plating current density is
varied within the range of 5 to 30 mA/cm.sup.2. When the plating
bath temperature is varied within the range of 25 to 35.degree. C.,
the content of Ni is slightly increased as the temperature is
increased, but the characteristics themselves are not affected.
The magnetic film of the present embodiment is suitable for an
upper magnetic core of an inductive head having a lower magnetic
core using an Fe-Ni series alloy containing Ni of 70 to 80 wt %,
but the film may be used both for the upper and the lower magnetic
cores.
Especially, as shown in FIGS. 16A, 16B and 16C, B.sub.S shows the
highest value of 1.6 T at Ni of 40 to 50 wt %, and it is preferable
to combine with a film having an (Ni/Fe) ratio of 0.667 to 1.00.
Incidentally, the (Ni/Fe) ratio of a film having Ni of 38 to 60 wt
% is 0.613 to 1.50.
FIGS. 17A, 17B and 17C show test results on the magnetic
characteristics and resistivity (.rho.) of a magnetic film
containing Mo in a (Ni 44 wt %-Fe) series alloy.
That is, the figure shows the magnetic characteristics and
resistivity (.rho.) of a magnetic film formed by adding Mo as an
element to the increase resistivity (.rho.) to a plating bath
containing N.sup.++ of 16.7 g/l and Fe of 2.2 g/l. The Mo is added
using Na.sub.2 MoO.sub.4.4H.sub.2 O by 5 g/l at a maximum.
It can be understood that resistivity (.rho.) of the magnetic film
is increased in proportion to the amount of added Mo. For example,
the resistivity (.rho.) of the magnetic film having Mo of 2 wt %
shows above 60 .mu..OMEGA..cndot.cm, which is about three times as
large as that of the 80Ni-Fe permalloy film.
In this case, the saturation magnetic flux density (B.sub.S) is
decreased by only 5% and nearly 1.50 T, which is 1.5 times as high
as that of the 80Ni-Fe permalloy film.
However, it is undesirable to add an amount of Mo exceeding 3 wt %
(Mo of 5 g/l on the base of Na.sub.2 MoO.sub.4.4H.sub.2 O) since
the magnetic coercive force in the hard axis direction (H.sub.CH)
becomes above 1 Oe and the saturation magnetic flux density
(B.sub.S) becomes below 1.5 T.
Adding Cr, instead of Mo, has been studied, and the results are
nearly the same as in the case of adding Mo. The magnetic film of
this example may be used in the same way as in the previous
examples.
FIGS. 18A, 18B and 18C show test results on an (Ni 44 wt %-Fe)-Co
15 wt %-Mo magnetic film to which Co and Mo are added at one time
in order to further increase the saturation magnetic flux density
(B.sub.S) and the resistivity (.rho.) without degrading the
magnetic characteristics of the magnetic film.
The Co is added using CoSO.sub.4.7H.sub.2 O, and the Mo is added
using Na.sub.2 MoO.sub.4.4H.sub.2 O, in the same way as discussed
with reference to FIGS. 17A-17C. The examples shown represent a
case where the amount of Co added is a constant of 13 wt % (100 g/l
on the base of CoSO.sub.4.7H.sub.2 O) and, on the other hand, the
amount of Mo added is varied up to 4 wt %.
As a result, by adding Co of 13 wt %, the saturation magnetic flux
density (B.sub.S) of the magnetic film is increased by 10% and
becomes 1.78 T. However, the resistivity (.rho.) is decreased by
30% and is 35 .mu..OMEGA..cndot.cm. By adding Mo, the resistivity
(.rho.) is recovered. By adding Mo of 2.5 wt %, the resistivity
(.rho.) is increased by nearly 20% on the contrary and becomes 55
.mu..OMEGA..cndot.cm.
In this case, the saturation magnetic flux density (B.sub.S) is
1.55 T, which is a slightly higher value than the film without Co.
Further, since the addition of Co increases the anisotropy of a
film, the magnetic characteristic of the film is stabilized.
The magnetic film of this example may be used in the same way as in
the previous examples.
FIG. 19 shows the permeability (.mu.) of the typical magnetic films
fabricated through the manufacturing methods described with
reference to FIGS. 16A-16C, 17A-17C and 18A-18C. In the figure, the
permeability is normalized with the value .mu. at a frequency of 1
MHz. For the purpose of comparison, the permeability (.mu.) of the
80Ni-Fe permalloy film is also measured. The thicknesses of all
films are 3 .mu.m.
For the films of this example having a resistivity of 48 to 60
.mu..OMEGA..cndot.cm, the frequency (f) where the permeability
(.mu.) decreases by 25% (that is, 75% of initial permeability) is
up to the range of 40 MHz to 70 MHz. This range is 3 to 5 times as
wide as the frequency of 15 MHz for the permalloy. It can be
understood that the frequency characteristics of the films of the
present invention represent a distinct improvement.
FIG. 20 and FIG. 21 are cross-sectional views showing an inductive
head having a two stage winding coil using the magnetic films
according to the present invention for the upper and lower magnetic
films in the embodiment of FIG. 1.
As shown in the figure, the thin film magnetic head 210 involves a
lower portion and an upper portion magnetic film formed of two
films 212 and 214 made of a magnetic material, for example,
permalloy. The films 212 and 214 are deposited in two stages
containing shaping films 221 and 213, respectively.
These films 212 and 214 are separated by insulating films 215, 216
and 217, except for a back portion region 218 where the films are
physically in contact and a top end region 219 where the films are
separated by a thin film 220 of a non-magnetic material to form a
magnetic gap 221.
There is provided a flat conductive coil 222 in the space between
the films 212 and 214 of a magnetic material. The coil 222 has two
inter-layer multi-windings 223a to 223n deposited in an elliptical
pattern between the films 215, 216 and 217 of insulating
material.
The top end portion of the transducer gap 221 is even with an air
bearing surface (ABS) formed on a non-magnetic substrate attached
to the above mentioned films.
The transducer gap 221 reacts with a rotating magnetic recording
medium (not shown), such as a rotating magnetic disk, in an air
bearing relation. When the disk is rotated, the head flies on the
air bearing surface (ABS) very near the recording surface of the
disk.
The thin film magnetic head is fabricated by depositing a magnetic
film 212 and a shaping film 211 on a substrate 224 using a proper
mask in order to form a thin deposited film in the top region 219
of a magnetic pole chip. Then, a non-magnetic film 220 is formed on
the films 211 and 212 except for the back gap region 218.
Then, a first insulating film 215 is deposited onto the film 220
except for the magnetic gap 221. A continuous and flat conductive
first film of elliptical swirl-shaped winding 223a to 223n is
deposited on the insulating film 215 through, for example,
electroplating.
An insulating film 216 is deposited on the first film of the coil;
a second film winding of the coil is deposited; and then, on the
coil an insulating film 217 is deposited. Then, as described above,
the magnetic film 214 is deposited on the insulated coil except for
the back portion gap region 218 which physically contacts the
magnetic film 212.
The top 219 of the magnetic pole chip has a pre-selected nearly
constant width W. The width W is equal to or slightly narrower than
the width of a track on the corresponding rotatable magnetic
medium.
The selected width W of the top end of the magnetic pole chip is
obtained by cutting the top end of the magnetic pole chip, and the
step to cut the top end of the magnetic pole chip is performed
before the step to deposit the shaping film 213 for the second
magnetic film 214. By changing the process in such a manner, the
top of the magnetic pole chip can be cut with a very much higher
accuracy than a conventional process.
After depositing the magnetic film 214 and before depositing the
shaping film 213, the thin film head assembly is covered with a
photo-resist mask 230. Then, a window 232 is formed on the
photo-resist mask in either of the sides of the top end region of
the magnetic pole chip of the head.
The masked head is subjected to an ion milling process. During the
process, the portion of head not covered by the mask is milled to
be shaped to have a desired width as shown in FIG. 5.
The ion milling process affects the surface to be worked in the
same manner as a normal condition, and accordingly a structure not
covered with the mask is also milled together with the photo-resist
mask. Therefore, the milled material produced from the head is
re-deposited onto the remaining portion of the mask and onto the
head structure which has been milled before.
For this reason, ion milling is performed in two stages. In the
first step, the un-masked structure is milled up to the substrate
224 through the magnetic film 14, the non-magnetic gap film 220 and
the magnetic film 212. In order to completely remove the material,
it is preferable that the first step is performed until the
substrate 224 is slightly milled.
The second step of the ion milling process is performed to remove
all the re-deposited materials, and is performed in a large angle
inclining state in which the surface inclines 75 to 80 degree to
the vertical direction. In a preferable embodiment of an ion
milling step, a permalloy magnetic material is milled with an
etching rate of about 550 .ANG. per minute by
electric power of about 2 watt per cubic centimeter. Then the
photo-resist is removed, a shaping magnetic film is deposited, and
thus a thin film magnetic head is completed.
The photo-resist mask is milled during ion milling, and the
thickness of the photo-resist on the head becomes thinner than the
thickness of the photo-resist on the magnetic pole chip region
depending on the shape of the magnetic film 214.
The thin film magnetic head fabricated according to the present
invention is of a yoke structure having a transducer magnetic gap
in one end and a back gap region in the other end, and the yoke
structure, having a conductive coil for energizing a magnetic yoke
attached between the magnetic gap and the back gap region of the
yoke structure, is formed with two films made of a magnetic
material.
A disk storage system constructed using the thin film magnetic head
fabricated according to the present invention will be described.
The example of the disk storage system according to the present
invention comprises a magnetic disk having an outer diameter of
approximately 3.5 inches, a spindle for rotating the disk, a
positioning mechanism for a magnetic head and a housing.
The magnetic head is an inductive head, and the track width is 5.0
.mu.m. The upper and the lower magnetic films of the head are
formed with (Ni 44 wt %-Fe)-2 wt % Mo alloy thin films having a
saturation magnetic flux density of 1.3 T, a resistivity (.rho.) of
60 .mu..OMEGA..cndot.cm, a relative permeability .mu. of 1000, a
film thickness d of 3 .mu.m, and a gap length of 0.4 .mu.m.
An equivalent effect may be obtained using the following material
for the magnetic pole, that is, a similar Ni-Fe series alloy having
a saturation magnetic flux density of 1.6 T, a Fe-Co-Ni/Al.sub.2
O.sub.3 /Fe-Co-Ni multi-layer film, a thin film of Ni-Fe containing
ZrO.sub.2, Y.sub.2 O.sub.3, HfO.sub.2, Al.sub.2 O.sub.3 or
SiO.sub.2 having a grain size of 2 nm to 3 nm.
In the case of mixing an oxide in the magnetic film, the grain size
is preferably 0.5 nm to 5 nm. This is because, when the oxide grain
size is within the above range, only the resistivity can be
increased without degrading the saturation magnetic flux density or
the soft magnetic characteristic so much.
By mixing an oxide as described above in the Fe-Ni alloy thin film,
the resistivity can be increased up to approximately 60
.mu..OMEGA..cndot.cm, and the relative permeability shows as a good
soft magnetic characteristic of nearly 1000.
On the other hand, in a case where a NiFe thin film without an
oxide is employed for a recording magnetic pole of a head, the high
frequency characteristic can be improved by decreasing the relative
magnetic permeability up to 500 or less. However, it is necessary
to set the recording magnetomotive force of a head to a value
larger than 0.5 T.
A recording film of a magnetic disk is formed of CoCrTa (adding
amount of Cr is 16 at %) having a magnetic coercive force in the
recording bit direction of 2100 Oe and a magnetic coercive force
orientation ratio of 1.2. The product Br.cndot..delta. of the
residual magnetic flux density and the film thickness of the
recording medium is 300 gauss.cndot..mu.m.
By employing the recording medium, it is possible to improve the
linear recording density characteristic and to substantially
decrease the medium noise in a high linear recording density range.
When the medium magnetic coercive force is lower than 200 Oe, the
bit error rate is decreased.
The rotating speed of the spindle during recording and reproducing
is set to 4491 rpm, and the amount by which the head floats at the
outermost periphery of the data recording region on the magnetic
disk at that time is 0.05 .mu.m.
The linear recording density on each track is set so becomes equal
from the inner most periphery to the outermost periphery of the
data recording region, and the recording frequency at the outermost
periphery is set to 67.5 MHz.
In the disk storage system in this embodiment, the linear recording
density of data on each of the tracks is set to 144 kBPI (kiro Bit
Per Inch), the track density is set to 5 kTPI (kiro Track Per
Inch), and accordingly areal density is 720 mega-bit per square
inch.
In this example, four magnetic disks are used, the format capacity
of the system is 2.8 giga-bytes, and the transfer rate is 15
mega-bytes per second.
Although in this example, 8/9 conversion is used for data
recording, a system having the same performance as this example may
be constructed even when the conventional 1-7 method is used for
data recording. However, in that case, the recording frequency
becomes 45 MHz.
The specification of the disk storage system constructed according
to this example is shown in Table 3.
TABLE 3 ______________________________________ Specification of a
3.5 inch Type Apparatus ______________________________________
Memory Capacity 2.8 GB Number of Disks 4 Number of Data Surfaces 8
Number of Heads 8 Number of Tracks/Disk Surface 4427 Maximum Linear
Recording Density 144 kBPI Track Density 5 kTPI Rotating Speed 4491
RPM Recording Frequency 67.5 MHZ Transfer Rate (to/from Media) 15
MB/sec ______________________________________
Description will be made on the results obtained from a disk
storage system combining a magnetic head according to the present
invention with magnetic disks having disk a diameter of 2.5 inches,
1.8 inches and 1.3 inches.
The magnetic head and the magnetic disks used in this example are
the same as those used in the previous example, the linear
recording density of data on each of tracks is set to 144 kBPI, and
the track density is set to 5 kTPI. The rotating speed of the
spindle is set so that the transfer rate becomes 15 MB/sec for each
of the disks.
Further, as described in the previous example, a system having the
same performance may be constructed even when the conventional 1-7
method is used for data recording. However, in that case, the
recording frequency becomes 45 MHz.
TABLE 4 ______________________________________ Specification of a
2.5 inch Type Apparatus ______________________________________
Memory Capacity 1.8 GB Number of Disks 4 Number of Data Surfaces 8
Number of Heads 8 Number of Tracks/Disk Surface 2951 Maximum Linear
Recording Density 144 kBPI Track Density 5 kTPI Rotating Speed 6376
RPM Recording Frequency 67.5 MHZ Transfer Rate (to/from Media) 15
MB/sec ______________________________________
TABLE 5 ______________________________________ Specification of a
1.8 inch Type Apparatus ______________________________________
Memory capacity 1.4 GB Number of Disks 4 Number of Data Surfaces 8
Number of Heads 8 Number of Tracks/Disk Surface 2213 Maximum Linear
Recording Density 144 kBPI Track Density 5 kTPI Rotating Speed 8982
RPM Recording Frequency 67.5 MHZ Transfer Rate (to/from Media) 15
MB/sec ______________________________________
TABLE 6 ______________________________________ Specification of a
1.3 inch Type Apparatus ______________________________________
Memory Capacity 0.9 GB Number of Disks 4 Number of Data Surfaces 8
Number of Heads 8 Number of Tracks/Disk Surface 1475 Maximum Linear
Recording Density 144 kBPI Track Density 5 kTPI Rotating Speed
13473 RPM Recording Frequency 67.5 MHZ Transfer Rate (to/from
Media) 15 MB/sec ______________________________________
Two kinds of inductive heads using magnetic poles having different
resistivity p, film thickness d and relative permeability .mu. were
fabricated, and the frequency dependence of the recording magnetic
field intensity for each of the heads was measured using an
electron beam tomography method.
The magnetic pole material, the magnetic pole thickness d, the
resistivity .rho. and the relative permeability .mu. in a low
frequency band below 1 MHz for each of the prototype heads are
shown in Table 7.
The head A comprises a magnetic pole formed of a Ni-Fe alloy single
film having the composition described with reference to FIGS. 1-15
and film thickness of 3 .mu.m. The head B comprises a magnetic pole
formed by laminating Fe-Co-Ni-Mo films of 2.2 .mu.m film thickness
through an Al.sub.2 O.sub.3 intermediate film of 0.1 .mu.m film
thickness, in the same manner as described with reference to FIGS.
18A-18C. Thereby, the total thickness of the magnetic pole film of
this head is 4.5 .mu.m.
Here, in the multi-layer film of Fe-Co-Ni-Mo/Al.sub.2 O.sub.3
/Fe-Co-Ni-Mo, when the thickness of the single layer of the
Fe-Co-Ni-Mo film exceeds 2.7 .mu.m, the attenuation of the magnetic
field intensity at a recording frequency of 45 MHz becomes above
10% to cause write blurring or fluctuation in an over-write film,
which is undesirable. In this example, the thickness of the
Fe-Co-Ni-Mo film is set to 2.2 .mu.m.
The head C comprises a lower magnetic film of a magnetic pole which
is a Co-Ta-Zr amorphous single layer film having a film thickness
of 3 .mu.m and a resistivity of 90 .mu..OMEGA..cndot.cm.
TABLE 7 ______________________________________ Specification of
Prototype Thin Film Magnetic Head
______________________________________ d .rho. Head Material of
Magnetic Pole (.mu.) (.mu..OMEGA..multidot.cm) .mu.
______________________________________ A NiFe 3.0 16 1000 B
FeCoNiMo multi-layer film 2.2 16 1000 C CoTaZr 3.0 90 1000
______________________________________ Note d: thickness of
magnetic pole .rho.: resistivity .mu.: relative permeability
The head efficiencies n are calculated from the measured results of
the normalized frequency dependence of the recording magnetic field
intensity. For the head A having a magnetic pole of a Ni-Fe single
layer film, the recording magnetic field intensity begins to
decrease near a point exceeding 10 MHz and the intensity at 100 MHz
is attenuated to lower than 60% of the intensity in the low
frequency band.
On the other hand, although the head B uses Fe-Co-Ni-Mn films
having a magnetic permeability and a resistivity equivalent to
those of the NiFe film used in the head A, the eddy current loss is
substantially decreased, since the films are of a multi-layer
structure through an Al.sub.2 O.sub.3 insulating film.
In the case of this head, the attenuation of the magnetic field
intensity at 100 MHz is nearly 20% and the frequency characteristic
is improved. In the case of the head C, the attenuation of the
magnetic field intensity at 100 MHz is nearly 0% and the frequency
characteristic is outstanding.
In another example of the present invention, upper and lower
magnetic films are formed by the following method.
There is fabricated an inductive head having upper and lower
magnetic cores which are electroplated through a mask in a plating
bath containing Ni.sup.++ of 16.7 g/l, Fe.sup.++ of 2.4 g/l, and a
common stress-release agent and a surface-active agent under a
condition of a pH of 3.0 and a plating current density of 15
mA.
The track width is 4.0 .mu.m, and the gap length is 0.4 .mu.m. The
composition of this magnetic film is 42.4 Ni-Fe (weight %), and as
to the magnetic characteristics, saturation magnetic flux density
(B.sub.S) is 1.64 T, the magnetic coercive force in the hard axis
direction (H.sub.CH) is 0.5 Oe, and resistivity (.rho.) is 48.1
.mu..OMEGA..cndot.cm.
FIG. 22 is a perspective view showing a dual element head, and FIG.
23 is a plan view of the head. The write head comprises an upper
magnetic core 320, a lower magnetic core 321 which also serves as
an upper shield film, and a coil 325. The read head comprises a
magnetoresistive element 323, an electrode 324 for conducting sense
current to the magnetoresistive element 323 and a lower shield film
322. The write and read heads are formed on a slider 326.
This inductive head is mounted on the disk storage system described
with reference to FIGS. 11-15 to evaluate the recording
performance. The medium used has an outer diameter of 3.5 inches
and a magnetic coercive force of 2500 Oe.
The performance (over-write characteristic) of the recording head
according to the present invention, when evaluated under such a
construction, shows an outstanding characteristic which is
approximately -50 dB at a high frequency band above 40 MHz.
A disk storage system in a further example of this invention
employs a dual element head, as shown in FIG. 22, which uses an
inductive head for recording and a magnetoresistive element for
reproducing. The upper magnetic film of the recording magnetic pole
of the inductive head is
formed as described above.
And, for the other of the upper shield film 81, also serving as a
recording magnetic pole, a multi-layer film of Fe-Co-Ni/Al.sub.2
O.sub.3 /Fe-Co-Ni having a single layer thickness of Fe-Co-Ni film
of 2.2 .mu.m is used. The thickness of the Al.sub.2 O.sub.3
intermediate film is set to 0. 1 .mu.m, and the track width of the
recording pole is set to 3 .mu.m.
A Ni-Fe alloy film having thickness of 1 .mu.m is used for the
lower shield film 82. A Ni-Fe alloy film having a thickness of 15
nm is used for the magnetoresistive element 86, which is driven
utilizing a soft film bias method.
Instead of the magnetoresistive element 86 using a Ni-Fe alloy
film, it is also possible to use a spin valve type element composed
of an Ni-Fe film, a Cu film, a Co film and an anti-ferromagnetic
film of Ni-o series, Fe-Mn series or Cr-Mn series; an alloy type
giant-magnetoresistive element of Co-Ag, Co-Au, NiFe-Ag, Co-Cu,
Fe-Ag or the like; or a multi-layer type giant-magnetoresistive
element of co/cr, Fe/Cr, co/cu or NiFe/Cu series.
The disk storage system constructed according to this example can
attain the same specification as shown in Table 2.
* * * * *